This invention relates to a magneto-resistance effect device (namely, an MR device), and in particular, to a magneto-resistance effect device which is capable of reproducing a desired recording information from a magnetic recording medium by the use of the magneto-resistance effect.
A magneto-resistance effect device (namely, an MR device) of the type described conventionally and widely has been used for a magnetic sensor, a magnetic head and an large-scale integrated circuit (namely, an LSI) memory.
Recently, a giant magneto-resistance (namely, GMR) effect has been developed, and has been widely applied for the industry field.
In this event, it has been conventionally and widely known that the spin scattering causes the magneto-resistance effect. Specifically, the phenomenon regarding the spin scattering results from the fact that an electron of up-spin has low scattering probability for an electron of the up-spin, and has high scattering probability for an electron of downspin.
In other words, the up-spin electron has low scattering probability in a magnetic domain of the up-spin while it has high scattering probability in different magnetic domain. As a result, the magneto-resistance effect takes place.
Therefore, it is required that a magnetization direction is variable in accordance with a change of a desired external magnetic field, and the domains of the up-spin and the down-spin coexist in the MR device in order to realize the MR effect in accordance with difference of the spin scattering. Namely, magnetization directions are different to each other in the respective domains.
In particular, when each magnetic domain has a magnetization direction of parallel opposite to each other, the MR effect indicates a maximum value. Therefore, it is important as a device parameter to realize the opposite parallel state under a low external magnetic field because the parameter relates to high sensitivity of the MR device.
Several methods have been so far reported in accordance with difference in structure to form the above-mentioned opposite parallel state.
For instance, devices, which utilize MR effect, are conventionally known, and are classified into (1) the MR devices formed by a granular film, (2) MR device formed by a metal multi-layer, (3) MR devices (magnetic bulb) of the spin-bulb type due to a sandwich structure via a tunnel barrier.
In the above-mentioned MR device formed by the granular film, ferromagnetic material, such as Fe, Co, and Ni, is precipitated or deposited in a non-magnetic layer, as disclosed in Japanese Unexamined Patent Publication No. Hei. 6-318749.
In this event, a precipitated state (namely, shape, size and direction of the precipitated particle) becomes irregular. More specifically, the precipitated particle has a long ellipse in accordance with a precipitated condition, and thereby, the size of the particle becomes random.
On the other hand, difference of one axis anisotropy or coercive force occurs for each precipitated particle by the randomness in size of the particles. Thereby, the MR effect brings about. At the same time, the magnetization is reversed under a low external magnetic field because the precipitated particle is small in size. In consequence, the MR device can operate under the low magnetic fields.
Subsequently, the MR effect due to the metal multi-layer has been disclosed in many papers. For example, the GMR effect caused by a multi-layer film consisting of iron and chromium is described in Physical Review Letter, 1998, volume 61, number 21, page 2472.
Further, the above-mentioned spin-bubble type MR device has been disclosed, for example, in Journal of Applied Physics, Aprl 1991, Vol. 69 (8), pages 4774-4779.
Specifically, MR devices having three layer structure have been suggested. In this case, the MR device utilizes the difference of the coercive force between a permalloy layer that is magnetically free and a permalloy layer that is magnetically pinned by a manganese layer.
However, ferromagnetic material, such as Fe, Co, and Ni, is precipitated in the non-magnetic electrical conductive layer in the conventional MR device of the granular type. In this event, it is difficult to control subtle differences of coercive force and precipitation particle density because the ferromagnetic material is naturally precipitated or deposited. In consequence, it is difficult to keep uniformity in manufacturing. As a result, the MR effect can not be essentially and sufficiently realized.
On the other hand, a large GMR effect of 200% or more at maximum is observed in the MR device of the metal multi-layer type. However, it is difficult to process the device because a current flows in a direction perpendicular to a plane.
Moreover, the resistance of the device is extremely low (approximately, several tens macro-ohm) because a practical device has a size of 0.24 micron in the perpendicular direction for the plane at several tens micron square.
In addition, an external magnetic field of several tesla is required to reverse the magnetization, and this is not a practical sensitivity.
Thus, there are a plurality of problems in putting conventional MR devices to practical use.